Deformation Behavior and TExture Evolution of Steel Alloys under Axial-Torsional Loading Page: 4 of 18
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tubes, rods, or prismatic sections. The effect of stress path (torsion versus tension or its
combination) on the stress-strain behavior and the potential anisotopic state of yield surface can
be obtained using procedures developed by Han and Penumadu [1]. The texture measurements
and its evolution as a function of loading path will also fill a critical intellectual gap in the
literature.
It is known that metallic materials exhibit variance in yield stress as a function of multi-axial
loading (for example: tensile versus torsion). Guest could be considered one of the first to study
elastic limits for multi-axially stressed metals, using thin tubes of steel, iron, and copper
subjected to torsion, torsion with tension, tension, internal pressure with tension, and solely
internal pressure [2-4]. Guest used the same sample to perform different stress path tests in this
loading scheme, which caused his yield points to be subsequently higher upon reloading and his
stress ratios, failure in shear to tension, to be ambiguous. Such an experimental approach also has
the limitation of uncoupling the combined effect of texture and loading path. In general, his
observations lead him to believe that the occurrence of plastic strain had little impact from the
intermediate principal stress but was determined by the absolute value of a principal shear stress
reaching a critical value [5]. Yu provides a comprehensive summary of past research that
attempted three dimensional testing, providing a summary on materials evaluated,
experimentally measured ratio of yield stress in shear to tension, and suitability of yield criteria
considering the yield surfaces proposed by von Mises, Tresca, and the one based on Twin shear
[6]. It shows that the discrepancies among different experiments and different materials are large
and results do not agree with established yield criteria and no general conclusions can be inferred
on suitability of a given yield criteria. Therefore, it is very important to choose a reasonable yield
criterion experimentally, even for simple slip plane systems, as the yield behavior is largely
controlled by its initial and evolving microstructure, processing and environmental conditions.
Up to now it is still a problem to find a unified yield criterion that can be applicable to more than
one kind of material, even when processed identically. Texture is largely ignored due to a lack of
reliable measurement techniques in the past such as neutron scattering methods to yield bulk
texture.
MATERIALS AND TESTING SYSTEM
Mechanical Testing System
A highly sensitive biaxial servo-hydraulic MTS mechanical testing system with a full-scale
capacity of 25 kN axial force and 250 N-m torque, shown in Fig. la, was used to perform
mechanical testing, applying tension and torsion simultaneously. An axial extensometer in
Fig. lb was used to record the on specimen axial strains from the deforming sample. The axial
force obtained from the biaxial MTS system was also verified by comparing with a uniaxial
tensile system having a 50 kN external load cell. The flat steel alloy samples were evaluated in
tension using two different MTS servo-hydraulic testing systems (a 25 kN biaxial system as
shown below and 100 kN axial MTS system) and results showed very high repeatability in
Figure 2a. Moreover, a custom made Universal Testing Machine (UTM) that used electrical axial
and torsional actuators developed by the senior author at the University of Tennessee in Figure
2b was also used to evaluate the accuracy of the biaxial MTS system and provided very similar
experiments stress-strain results. Thus, it was concluded that the use of biaxial testing system for
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Siriruk, A.; Kant, M.; Penumadu, D.; Garlea, E. & Vogel, S. Deformation Behavior and TExture Evolution of Steel Alloys under Axial-Torsional Loading, article, June 1, 2011; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc832818/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.